Patients with cystic fibrosis (CF) have a high incidence of diabetes mellitus (DM) and glucose intolerance. The impact of CF/DM on the morbidity and mortality of CF is not well understood. The hypothesis of the study is that the degree of insulin resistance will be correlated with negative clinical outcome. Insulin sensitivity in CF patients with and without DM will be measured and compared, along with controls. The degree of insulin sensitivity/resistance will be correlated with clinical outcome.